Solvent extraction process



Dec. 19, 1961 C. N. KIMBERLIN, JR., ETAL SOLVENT EXTRACTION PROCESS Filed May 20, 1958 LIGHT GASES FRACTIONATION SYSTEM NAPHTHA LIGHT GAS OIL 2 Sheets-Sheet 1- ,SOLVENT STRIPPER HEAVY GAS OIL RESIDUAL GAS OIL FIGURE I BUTYROLACTONE SOLVENT EXTRACTION SYSTEM SOLVENT STRIPPER EXTRACT OIL Charles N. Kimberlin, Jr. William J. MoHox B W41. Attorney Inventors Dec. 19, 1961 SOLVENT EXTRACTION PROCESS Filed May 20, 1958 2 Sheets-Sheet 2 FIGURE .11

ISOMERIZATION ISOMERIZED UNIT\ PRODUCT W a 58 I I as f 68 iv 62 EXTRACTION\ T 5o RAFFINATE -60 52 BENZENE c /c OR f c FRACTION T 54 -D|STILLATION 5e EXTRACT SOLVENT Charles N. Kimberlin, Jr. wiuiqm Muttox Inventors By WwM A y c. N. KIMBERLIN,-JR., ETAL 3,013,962

United States Patent 3,013,962 SOLVENT EXTRACTION PROCESS Charles Newton Kimberlin, Jr., and William Judson Mattox, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed May 20, 1958, Ser. No. 736,547 8 (llaims. (Cl. 208-254) The present invention concerns a novel solvent extraction process employing lactones, and preferably butyrolactone as a solvent for upgrading of petroleum fractions. More specifically, the present invention relates to the extraction of hydrocarbons and hydrocarbon mixtures with a solvent comprising butyrolactone. In one of its modifications, the present invention is of particular utility in the treatment of gas oil fractions derived from a crude petroleum oil so as to improve substantially the characteristics of the gas oil for processing by catalytic cracking. The extraction process of the present invention is notable in providing a technique for the selective extraction of metal contaminants, condensed ring aromatic compounds and nitrogen compounds normally present in high boiling petroleum oil fractions.

The present invention is a continuation-in-part of Serial No. 554,867, filed December 22, 1955, which in turn, is a continuation-in-part of Serial No. 491,322, filed March 1, 1955, now U.S. Patent No. 2,913,394, issued November 17, 1959.

In recent times, a great deal of effort has been applied in the petroleum refining field to increase the recovery of catalytic cracking feed stock fro-m residual fractions of petroleum oil. Conventionally, the feed stock to a catalytic cracking operation constitutes a so-called gas oil fraction of crude oil which boils in the range of about 400 to 800 F. or somewhat higher. Portions of the petroleum crude oil boiling above the gas oil boiling range may be considered residual petroleum fractions. Such residual fractions may be used as sources of asphalt, fuel, and other products which are of relatively low economic value. It, therefore, becomes attractive to develop means for successfully utilizing portions of the residual fractions of crude oil as catalytic cracking feed stock.

Attempts to employ heavier fractions of crude oil for catalytic cracking have been limited heretofore due to the presence of certain metal contaminants in such heavy fractions. Thus the highest boiling fractions of a crude oil contain substantial portions of metal contaminants, particularly, including nickel, vanadium and iron compounds. The residual fractions of typical crude oils generally contain these metal contaminants in quantities of about 10 to 50 pounds per 1000 barrels of metal contaminants. When an attempt is made to segregate higher boiling distillate fractions of a crude oil, some portion of these metal contaminants is inherently and unavoidably carried over into the distillate products. For example, in a vacuum distillation operation where a heavy boiling gas oil fraction is segregated from a crude oil, about 0.5 to 10 pounds per 1000 barrels of metal contaminants will be obtained in the gas oil distillate in a typical situation. In this example, the gas oil distillate referred to would have a boiling range of about 800 to 1100 F., or higher.

The problem of metal contaminant carry over in the segregation of heavy distillate fractions is apparently due to two phenomena. First of all, it appears that the metal contaminants occur or are converted during distillation to the form of metal complexes. These complexes may generally be identified as large condensed rings constituents. Some of these metal complexes and particularly nickel and vanadium porphyrins are sufliciently volatile so as tobe carried overhead at a temperatureof about 1050 F. Consequently, when attempting to segregate Patented Dec. 19, 1961 high boiling gas oil fractions including components boiling above about 900? F., volatile metal contaminants are unavoidably obtained in the distillate product. It appears that a second phenomenon is also involved which may be referred to as mechanical entrainment. To generally indicate the mechanism of this effect, it can be considered that a small portion of high boiling liquid hydrocarbons from the residual fraction is normally entrained overhead in a distillation operation. Since such liquid hydrocarbons contain concentrated amounts of metal contaminants, such entrainment in distillate products accounts for a portion of the metal contamination of such distillates.

By virtue of the fact that catalytic cracking operations are adversely affected by the presence of such metal contaminants, it is apparent that the need exists for some means to recover high boiling fractions of a crude oil while eliminating contamination in the manner described. The presence of metal contaminants and particularly nickel and/ or vanadium in a catalytic cracking operation results in direct contamination of the catalyst by the metal compound. Metal continues to accumulate on the beta lyst during the life of the catalyst having the result of seriously alterin-gthe catalytic properties of the catalyst. One of the eifects of such catalyst poisoning is to cause excessive hydrogen to be produced during, catalytic cracking as the result of the change in the cracking characteristics of the catalyst. In actual commercial o erations hydrogen production has become so severe, due to catalyst poisoning, as to cause failure of gas compressors due to the change in the density of the gases, resulting in flooding of light end fractionation equipment and the like. It is to be understood, therefore, that the problem of catalyst contamination is a pressing problem at the present time. I It has been appreciated that one technique for prevent ing the problem of catalyst contamination could co'nceivably be a selective solvent treatment for the catalytic cracking feed stock in order to remove metal contaminants which are normally present. Hereto fore, however, difficulties have been encountered in finding a solvent capable of selectively removing metal contaminants. A solvent such as phenol or furfural which exerts a stro ng solvent action for high molecular weight aromatic compounds will also remove metal contaminants to some extent; However, the problem with such solvents is that they exhibit poor selectivity, resulting in substantial removal of hydrocarbon constituents as well as metal contamii nants. As a result, use of such solvents. has heretofore been economically prohibitive due to the loss in catalytic v cracking feed stock. I v v p g The present invention, in one of its embodiments and.

aspects, is based on the discovery that lactones, and

particularly butyrolafctone are uniquely eifective irriselecftively removing metal contaminants from heavy petroleum As a result, use of butyrolact'one ntakes" I normally present in the cracking feed stock. In particular, butyrolactone serves to remove condensed; ringare} matic compounds and nitrogen compounds" concomitant with removal of metal contaminants so as to. substantially improve the cracking characteristics of a feed stock treated with butyrola'ctone. V

The precise mechanismby which butyrolactone exhibits these specific and unusual solvent properties is not known at the' present time. It seems: probable, however, that the'particular molecularconfiguration of this compound combines a critical balance between hydrocarbon solubility and solvent power for the compounds enumerated which is particularly adapted for the purposes of this invention. It has been established, for example, that butyrolactone exerts solvent powers in the practice of this invention completely distinct from those of other solvents which have been used, such as furfural. It is to be understood, therefore, that in the practice of this invention butyrolactone specifically is to be employed as the selective solvent.

At the same time, however, it is possible to employ solvent modifiers with butyrolactone for particular applications. Such solvent modifiers are chosen so as not to substantially affect the selective solvent action of butyrolactone while changing somewhat the oil solubility characteristics of butyrolactone. Solvent modifiers are particularly useful for permitting extraction with butyrolactone at higher temperatures than normally attractive. Included among solvent modifiers which may be employed are water, aliphatic alcohols, acetic acid, and ethylene glycol or other glycols. Such compounds can be employed by combination with butyrolactone in minor amounts providing a solvent composition in which the solvent modifiers are present in amounts less than about one third of the total solvent composition.

Solvent extractions employing butyrolactone in accordance with one embodiment of this invention may be conducted at temperatures in the broad range of about 80 to 500 F. However, the selectivity properties of butyrolactone are not critically affected by tmeperature so that it is generally preferred to operate at moderate temperatures selected to maintain the feed stock at a suitable viscosity for treatment. Thus, in general, a temperature of about 100 to 200 F. is particularly attractive. The extraction can be conducted at any pressure selected from the broad range of about to 750 psi. Again, however, pressure is not particularly critical in the conduct of this invention, making it possible to conduct the process at atmospheric pressure as is normally preferred.

The amount of solvent composition employed in the practice of this invention varies somewhat in accordance with the feed stock to be treated and the degree of change required in the properties of the feed stock. In general, however, the amount of solvent to be employed will be selected from the range of 0.5 to 3 volumes of solvent per volume of oil to be treated. For most applications it is particularly preferred to use about 1 volume of solvent per volume of oil to be treated.

The solvent treating process may be carried out by conventional solvent extraction techniques. Thus, if desired, batch mixing and settling may be employed or continuous and countercurrent treating operations may be employed. In this connection, for example, it is particularly preferred to carry out the process by introducing butyrolactone at an upper portion of a treating tower to flow downwardly countercurrent to the oil to be treated which is introduced near the bottom of the treating tower. Packing elements, perforated plates, or other contacting aids can be employed in such a system. A raflinate phase constituting the treated oil and minor portions of butyrolactone may be removed overhead from such a tower. An extract phase, principally constituting butyrolactone together with minor amounts of constituents removed from the treated oil, can be removed from the bottom of the treating tower.

Solvent may be recovered from the rafiinate and extract phases by conventional techniques. Thus, solvent can be stripped from the extract and raflinate by a simple distillation procedure permitting removal of butyrolactone as an overhead product for recycle to the solvent treating system. Alternatively, and as a particular feature of this invention, solvent may be recovered by cooling the extract and ratfinate phases substantially below the extraction temperature. Cooling in this manner results in a change in solvent properties sutficient to liberate butyrolactone for recycle to the extraction system.

Alternatively, solvent may be recovered by adding water to the extract and raffinate phases. The addition of water causes the separation of an upper oil layer and a lower layer comprising an aqueous solution of butyrolactone solvent. The lower, aqueous solvent layer is withdrawn and may be dehydrated by distillation or other means for recycling to the extraction zone.

As indicated, solvent extraction employing butyrolactone is particularly attractive for the upgrading of catalytic cracking feed stocks. Such feed stocks may be defined as the gas oil fraction of a petroleum crude oil boiling above the gasoline boiling range or boiling above about 450 F. The end point of such a gas oil fraction can be as high as desired, ranging upwardly to about 1050 to 1300 F. (equivalent atmospheric boiling point). It may be observed that solvent extraction of a lubricating oil distillate boiling within the gas oil boiling range as defined is also particularly attractive. Employing the process of this invention, such a solvent extraction serves to remove undesired aromatic compounds from a lubricating oil so as to provide high yields of high quality lubricating oil.

While, as indicated, in accordance with one of its aspects the invention is broadly applicable to extraction of gas oil boiling in the range of about 450 to 1300 F., this embodiment of the invention is of particular application to the portion of such fractions boiling above about 900 to 950 F. Such high boiling gas oil fractions are those in which metal contaminants are particularly concentrated. For this reason, in preparing catalytic cracking feed stock it is particularly preferred to segregate the portion of the feed stock boiling above about 950 F. and then to subject this specific fraction to the process of this invention.

The accompanying drawing illustrates a specific and preferred embodiment of the present invention showing its application to the preparation of catalytic cracking feed stock.

Referring to FIGURE I, the number 1 is used to designate a fractionation system of the type conventionally used in segregating crude oil into fractions of different boiling range. Fractionation system 1 may constitute a combination of an atmospheric distillation unit and a vacuum distillation unit or may comprise other types of distillation equipment adapted to provide the separate fractions to be identified. The fractionation system is of the character permitting segregation of a crude oil introduced through line 2 into the products identified on the drawing. C and lighter gases may be removed overhead through line 3 and a naphtha fraction may be removed as a side stream product through line 4. Preferably a light gas oil stream boiling in the range of about 450 to 950 F. is removed as a higher boiling side stream product through line 5. Finally, the highest boiling side stream product, removed through line 6, is a heavy gas oil boiling in the range of about 950 to 1300 F. Heavy residual oil constituents are Withdrawn from the fractionation system through bottom withdrawal line 7.

In accordance with this invention, the heavy gas oil fraction of line 6 containing substantial portions of metal contaminants is subjected to solvent extraction in tower 8. Butyrolactone is introduced to extraction system 8 through line 9 for countercurrent contact with the heavy gas oil in the tower. Extraction can be conducted for example at a temperature of about F., at atmospheric pressure and using about 1 volume of butyrolactone per volume of heavy gas oil.

The raftinate phase constituting treated oil together with small amounts of butyrolactone, is removed overhead from extraction system 3 through line 10. Residual solvent can be removed overhead from the treated oil in stripping zone 11, permitting removal of segregated butyrolactone through line 12 for recycle to line 9. A treated oil freed of residual solvent is then passed through line 13 to the catalytic cracking system 14.

. cyclone separators.

The extract phase removed from the solvent extraction system 8 through line 15 may similarly be passed to a solvent stripper 16 permitting removal of butyrolactone through overhead line 17. An extract oil will be withdrawn from the bottom of stripper 16 through line 18. This extract oil may be blended with fuel oil or can be employed as a source of chemicals or the like.

The treated oil of line 13 which is subjected to catalytic cracking is of improved cracking characteristics by virtue of the substantial elimination of metal contaminants. In addition, this oil is of better cracking characteristics because of the elimination of high molecular weight condenscd ring aromatic compounds and nitrogen compounds. This treated oil can be subjected to conventional catalytic cracking in zone 14. Thus, the cracking may be of the fixed-bed, suspensoid, moving bed or fluidized solids type. It is preferred, however, to employ a fluidized solids cracking process.

The fluidized solids technique for cracking hydrocarbons comprises a reaction zone and a regeneration zone, employed in conjunction with a fractionation zone. The reactor and the catalyst regenerator are or may be arranged at approximately an even level. The operation of the reaction zone and the regeneration zone is preferably as follows:

An overflow is provided in the regeneration zone at the desired catalyst level. The catalyst overflows into a withdrawal line which preferably has the form of a U- shaped seal leg connecting the regeneration zone with the reaction zone. The feed stream introduced is usually preheated to a temperature in the range from about 500 to.65 F., by heat exchange with regenerator flue gases which are removed overhead from the regeneration zone, or with cracked products. The heated feed stream is then introduced into the reactor. The seal leg is usually sufiiciently below the point of feed oil injection to prevent oil vapors from hacking into the regenerator in case of normal surges. Since there is no restriction in the overflow line from the regenerator, satisfactory catalyst flow will occur as long as the catalyst level in the reactor is slightly below the catalyst level in the regenerator when the vessels are maintained at about the same pressure. Spent catalyst from the reactor flows through a second U-shaped seal leg from the bottom of the reactor into the bottom of the regenerator. The rate of catalyst flow is controlled by injecting some of the air into the catalyst transfer line to the regenerator.

The pressure in the regenerator may be controlled at the desired level by a throttle valve in the overhead line from the regenerate-r. Thus, the pressure in the regenerator may be controlled at any desired level by a throttle valve which may be operated, if desired, by a differential pressure controller. If the pressure differential between the two vessels is maintained at a minimum, theseal legs will prevent gases from passing from one vessel into the other in the event that the catalyst ltlow in the legs should cease.

The reactor and the regenerator may be designed for high velocity operation involving linear superficial gas velocities of from about 2.5 to 4 feet per second. However, the superficial velocity of the upfiowing gases may vary from about 1 to feet per second and higher. Catalyst losses are minimized and substantially prevented in the reaction by the use of multiple stages of cyclone separators. The regeneration zone is also provided with These cyclone separators usually include 2 to 3 or more stages.

Distributing grids may be employed in the reaction and regeneration zones. Operating temperatures and pressures may vary appreciably depending upon the feed stocks being processed and upon the products desired. Operating temperatures are, for example, in the range from about 800 to 1000 F., preferably about 850 to 950 F. in the reaction zone. Elevated pressures may be employed, but in general, pressures below 100 pounds per square inch gauge are utilized. Pressures generally in the range from 1 to 30 pounds per square inch gauge are preferred. Catalyst to oil ratios of about 3 to 10, preferably about 6 to 8 by weight, are used.

The catalytic material used in the fluidized catalyst cracking operation are conventional cracking catalysts. These catalysts are oxides of metals of groups II, III, IV and V of the periodic table. A preferred catalyst comprises silica-alumina wherein the weight percent of the alumina is in the range from about 5 to 20%. Another preferred catalyst comprises silica-magnesia where the weight percent of the magnesia is about 20 to 35%.

The size of the catalyst particles is usually below about 200 microns. Usually at least 50% of the catalyst has a micron size in the range from about 20 to 80. Under these conditions with the superficial velocities as given, a fluidized bed is maintained where, in the lower section of the reactor, a dense catalyst phase exists while in the upper area of the reactor at disperse phase exists.

Included in the catalytic cracking system is a product fractionator adapted to segregate gasoline and heavier boiling fractions of the cracked product.

In the particular embodiment of the invention illustrated in the drawing, the heavy gas oil fraction is subjected by itself to extraction with butyrolactone so as to improve the cracking characteristics of the heavy gas oil. The light gas oil, withdrawn from fractionation system 1 through line 5, can be passed directly to catalytic cracking system 14. Alternatively, however, a part or all of this light gas oil can be extracted with the heavy gas oil in extraction zone 3. It is particularly preferred to cmploy a minor portion of light gas oil in admixture with heavy gas oil so as to reduce the viscosity of the gas oil to the extent desired.

The following examples illustrate the nature and utility of this embodiment of the invention:

EXAMPLE 1 A heavy gas oil having a 50% boiling point of 950 F. and a final boiling point above 1100 F. derived from a South Louisiana crude oil was subjected to the process of this invention. This gas oil contained 2.3 p.p.m. of nickel and 0.2 p.p.m. of vanadium prior to treatment. The oil was treated in a batch extraction with butyrolactone in three treatments employing 1 volume of butyrolactone per volume of oil in each treatment at a tem perature of 180 F. and at atmospheric pressure. Contacting by mechanical agitation for 5 minutes followed by settling for 5 to 10 minutes was adequate for this batch type of extraction. Solvent stripping from the rafiinate product provided 21 treated oil yield of 87%. This oil had a nickel concentration of only 0.25 p.p.m. and 0.0 p.p.m. of vanadium. It will be seen from these data that the extraction process of this invention is particularly adapted for substantially eliminating metal contaminants from heavy gas oils while providing high yields of treated oil. For comparative purposes, it may be noted that in a similar extraction with phenol as solvent, and with minor amounts of water added to regulate oil solubility, substantially poorer results were obtained. In this case oil yields of only 72% were obtained when treated to the same nickel content. Extraction with furfural to 0.25 p.p.m. of nickel yielded only 77% of oil. It is to be seen, therefore, that butyrolactone was effective in reducing the mckel'content of the treated oil to every 10w concentration and that the treated oil yields were much higher than when the extraction was made with conventional solvents such as phenol or furfural. a

EXAMPLE 2 The heavy South Louisiana gas oil employed in Example, 1 was contacted with 90% butyrolactone-l0% (0.25 to 1.0 ppm.) show the same selectivity an resulted from the use of 100% butyrolactone as solvent.

EXAMPLE 3 Butyrolactone extraction of South Louisiana gas oil was carried out at 100 F., by diluting the heavy oil with two volumes of a light hydrocarbon fraction (C Three batch extractions followed by flashing 005 the diluent yielded 94 weight percent of refined oil having a nickel content of 0.49 ppm. This yield is 13% higher than re sulted from phenol extraction to the same nickel content.

Table II MULTIPLE BATCH EXTRACTION OF HEAVY CATALYTIC CYCLE OIL [Tcinp.200 F.; pressureatrn.

Ratlinatc Vol. Percent Ext. No. of Yield VSO Solvent Wt. Gravity, Viscosity Vis.-Gr.

Total Percent API Index Constant Feed 0 100 17.0 103. 3 38. 8 59. 1 0. 925

BUTYROLACTONE SOLVENT 90% PHENOL SOLVENT EXAMPLE 4 In order to establish other solvent properties of butyrolactone, a variety of hydrocarbon oils containing nitrogen compounds was extracted with butyrolactone. The feed stocks employed and the results of these extractions are summarized in the following table.

Table I EXTRACTION OF NITROGEN-CONTAINING oILs It will be observed from these data that butyrolactone exerted a selective solvent action for the nitrogen compounds present in the various oils treated. As an example of the significance of these data, it will be noted that extraction of the heavy gas oil with butyrolactone provided :1 treated oil in yields of 83% While achieving 85% removal of nickel contaminants, 100% removal of vanadium contaminants, and while dropping the concentration of nitrogen compounds from 0.38 to 0.20%.

EXAMPLE 5 In order to show the versatility of the solvent properties of butyrolactone, a heavy catalytic cycle oil boiling It will be observed from these data that extraction with butyrolactone was operated to effectively remove undesirable lubricating oil constituents so as to provide high quality, high viscosity index lubricating oil. In considering these data, it is of particular interest to consider comparative extraction results employing phenol as an extraction agent. In this case, yields of equivalent quality lubricating oil (140 viscosity index) were obtained in amounts only 73% of those obtainable by the process of this invention. The quantity of butyrolactone solvent required to produce a given improvement in viscosity index was much lower than the amount of phenol needed to effect the same improvement. These comparative requirements are shown in the following tabulation:

Table 111 Butyrolactone Phenol 59 (Feed) O 0 45 100 It will be appreciated from the data presented that the process of this invention is a versatile and attractive process for upgrading petroleum fractions boiling in the gas oil boiling range. As described, the process is particularly attractive for preparation of catalytic cracking feed stocks and for manufacture of high quality lubricants.

A further very important embodiment of the present invention is the use of the lactone solvent of the present invention in the removal of aromatics and olefinic contaminants in isomerization feed streams. The isomerization of normal parafiins and slightly branched paratfins having 4 to 10 carbon atoms per molecule to more highly branched chain molecules is a well known process. catalysts normally employed are the Friedel-Crafts type such as AlCl AlBr BF and the like, promoted and activated generally by a hydrogen halide and/or other promoter. Normally, temperatures in the range of 200 to 420 F. are employed when A101 is the catalyst, and 32 to 100 F. when the more hydrocarbon-soluble AlBr is used. These catalysts are, generally supported on carriers such as Porocel, bauxite, alumina, active char, and the like. Liquid phase processes are preferred.

An important problem involved in the isomerization of hydrocarbons by these catalysts is the fact that aromatics, and particularly benzene, have a pronounced inhibitory effect on the isomerization. As little as 0.2 to 0.3% of benzene in the feed to an isomerization zone of the aluminum halide type shortly inhibits the reaction completely. It is necessary, therefore, to limit the amount of aromatics, and in particular benzene, in the feed to the isomerization zone to a level below a maximum of about 0.1%. Olefins, likewise, but to a less extent, have a deactivating elfect upon the catalyst, causing sludging.

In accordance with this embodiment of the present invention, lactones, and in particular ot-butyrolactone, have been found to. be an excellent extracting agent for aromatics and olefins which appear in small but deactivating amounts in isomerization feeds.

A schematic means of accomplishing this is shown in FIGURE II. A naphtha fraction consisting substantially of e o, normal parafiins, such as a virgin naphtha boiling in the range of from 80 to 220 F. is passed via line 52 into extraction zone 50. This zone may be of the liquid-liquid type previously described. Preferably, extratcion zone 50 is an extractive distillation Zone, wherein solvent/ naphtha ratios may be varied within the approximate range of 0.3 to 5 depending on the aromatic content and boiling range of the naphtha feed. Atmospheric or near atmospheric pressures will usually be preferred although sub-atmospheric to about 100 p.s.i.g. may be employed. Extractive distillation offers the distinct advantages of a simplified extraction operation in conventional type distillation equipment, the operation of which is already familiar to refinery personnel. In addition, solvent circulation rates are lower and treated naphtha yields are higher than with liquid-liquid extraction.

The extract phase resulting from the extractive distillation of the light virgin naphtha is passed via line 54 to distillation zone 56 where an overhead stream consisting essentially of benzene is withdrawn and preferentially blended with the isomerizate, thereby adding an important high octane blending agent to that material. Recovered lactone is passed via line 58 back to the extraction step.

The raffinate, substantially completely depleted in benzene and olefins, is now passed to isomerization zone 64 where, in the presence of 'AlBr preferably supported on Porocel, and preferably promoted with hydrogen bromide, the normal pentanes, hexanes, their mixtures, and/ or heptanes, are converted in high yield to the corresponding isomers. Liquid phase operation is employed and preferred operating conditions are, for aluminum bromide-Porocel in a suitably packed reactor in the presence of a hydrogen halide promoter, temperatures in the range of 50 to 120 F. and pressures of from about 5 to 100 p.s.i.g. To prevent cracking and disproportionation during the isomerization reaction, it is desirable to employ a cracking inhibitor. For a feed comprising C and C parafi'in hydrocarbons, from about to 20% of naphthenic hydrocarbons, such as methylcyclopentane or cyclohexane, should be present in the feed. For C paraffins, the amount of naphthenes should be somewhat higher. The Porocel or other support should contain on the order of 5 to 10% aluminum bromide which may be conveniently introduced by dissolving it in the initial portion of the feed. The amount of AlBr in the feed may The then be reduced to about 0.1% which will serve as makeup for the small amount of bromide that tends to dissolve in the reaction products and thus be carried from the reaction zone. The feed is conducted through the reaction zone at rates of the order of 0 .1 to 2 v./v./hr. As previously stated, reaction temperatures of from about 50 to 120 F. are employed, although a range of from about 60 to F. is preferred for maximum production of highly branched isomers.

The product from the isomerization zone is then withdrawn through lines 66 and 68' and, as pointed out, preferably combined with the aromatics originally present in the feed.

The use of butyrolactone as an extractive gasoline sol-. vent has been described in connection with catalytic reforming, hydroforming and isomerization. It is also advantageously employed in the extraction of thermal or catalytically cracked naphthas wherein substantial amounts of high octane value olefins are formed. Buty rolactone has the distinct advantage of being operable with olefin-containing feeds which heretofore could not be handled with such conventional solvents as sulfur dioxide.

The further advantages of the present invention are readily apparent from the illustrated examples below.

EXAMPLE 6 This example demonstrates the excellent results obtained in the extractive distillation of an isomerization feed with u-butyrolactone.

Extractive distillation tests were made on C virgin naphtha fractions in a 40plate Oldershaw column with butyrolactone solvent. High yields of raflinates were obtained which contained only 0.02% or less of benzene. Data from these tests are summarized in the following tabulation.

EXTRACTIVE DISTILLATION OF Cg ISOMERIZATION FEEDS [AG-plate Oldershaw column; butyrolactone solvent] solgelntl Raffinate 1 Naphtha Feed Ratio Vol. Percent Percent Benzene The extraction of each of these feeds with one volume of solvent/volume of naphtha yielded 92 to 94% of rafiinate having only 0.01 to 0.02% benzene. Increasing the solvent ratio to 2/1 increased the extract yield to 16-17% but did not further decrease the benzene cona tent of the raifinate. Small scale isomerization tests showed the. treated naphthas to be entirely satisfactory forthis conversion. This was shown by isomerization of the rafiinate over an AlBr -Porocel catalyst at room temperature to give a 91% conversion of the C paraflins to isohexanes.

EXAMPLE 7' The data given below is illustrative of the two methods of solvent extraction, (1) liquid-liquid extraction in an eleven-stage York-Scheibel'column at 80 F., and (2) extraetive distillation in a 40-plate Oldershaw column. Isomerization of the rafrinate was carried out over 20% AlBr -40% Porocel at 78 F. at atmospheric pressure for four hours. The benzene removed was recovered in this experiment by addition of water to the extract but distillation would offer no problem since there is a boiling point difference of over 200 F. between benzene and the solvent.

What is claimed is:

1. An improved proces for removing nitrogen compounds from a relatively heavy petroleum oil which comprises, contacting said oil with butyrolactone so as to concentrate nitrogen compounds in said butyrolactone, and separating a treated oil of substantially reduced con centration of nitrogen compounds.

2. The process of claim 1 wherein a solvent modifier is J employed in addition to said butyrolactone.

3. The process of claim 1 wherein said petroleum oil is selected from the group consisting of raw shale oil, at least partially hydrogenated shale oil and heavy gas oil.

4. An improved method of removing nitrogen compounds from an oil selected from the group consisting of raw shale oil, at least partially hydrogenated shale oil, and

12 heavy gas oil, which comprises, contacting said oil with butyrolactone so as to concentrate nitrogen compounds in said butyrolactone, and separating a treated oil having a reduced concentration of nitrogen compounds.

5. The improved method of claim 4 wherein a minor portion of water is employed as a butyrolactone solvent modifier.

6. An improved process for refining shale oil which comprises, extracting said shale oil with butyrolactone, and segregating a treated oil having a substantially reduced concentration of nitrogen compounds.

7. The process of claim 6 wherein said shale oil comprises raw shale oil.

8. The process of claim 6 wherein said shale oil comprises at least partially hydrogenated shale oil.

References Cited in the file of this patent UNITED STATES PATENTS 2,324,295 Goldsby et a1 July 13, 1943 2,507,861 Manley May 16, 1950 2,731,506 Love et a1 Jan. 17, 1956 2,741,578 McKinnis Apr. 10, 1956 2,754,248 Wetzel July 10, 1956 2,803,685 Pofienberger et al Aug. 20, 1957 2,831,905 Nelson Apr. 22, 1958 2,846,358 Bieber et al. Aug. 5, 1958 

1. AN IMPROVED PROCESS FOR REMOVING NITROGEN COMPOUNDS FROM A RELATIVELY HEAVY PETROLEUM OIL WHICH COMPRISES, CONTACTING SAID OIL WITH BUTYROLACTONE SO AS TO CONCENTRATE NITROGEN COMPOUNDS IN SAID BUTYROLACTONE, AND SEPARATING A TREATED OIL OF SUBSTANTIALLY REDUCED CONCENTRATION OF NITROGEN COMPOUNDS. 